1. Field of the Invention
The present invention relates generally to sealing apparatus and more particularly to apparatus for sealing a track shoe for endless tracks of a tractor-type vehicle.
2. Description of the Prior Art
Heretofore, within apparatus for sealing track shoes for endless tracks of tractor-type vehicles, it has been found that while one type of apparatus exhibits good sealing properties the same apparatus cannot accommodate thrust forces, and while another type of apparatus can accommodate thrust forces, the same exhibits poor sealing properties; and still further, in the case of an apparatus having acceptable sealing properties and being able to withstand and accommodate thrust forces, the apparatus nevertheless does not prevent earth and sand brought about or interposed between the end surface of the bushing and the seal from invading or penetrating interiorly of the apparatus in the form of wedge which will tend to deleteriously affect the sealing properties of the apparatus.
For example, as shown within FIG. 1, when use is made of a seal made of polyurethane rubber a, which exhibits relatively good sealing properties, and foamed polyurethane b, the apparatus has the disadvantage that it has been unable to receive or withstand strong thrust forces whereupon the same is substantially poor in wear resistance, especially of the foamed polyurethane rubber b, and in addition, the elasticity of the same is lost upon absorbtion of muddy water and subsequent drying of the same.
Similarly, as shown within FIG. 2, when use is made of a pair of leaf springs c, such apparatus has been able to absorb thrust forces, however, because the contact of the sealed surface is substantially linear contact, this apparatus has exhibited poor sealing properties.
As illustrated within FIG. 3, when use is made of a bellows-type seal of rubber, such as, for example, a hard urethane rubber or a metal, the same has demonstrated a relatively good capacity for receiving thrust forces and has exhibited acceptable sealing properties, however, because the surface pressure transmitted from the contacting surface of the bushing to the contacting surface of the seal is high, a bellows-type seal wears rapidly and in fact a portion S thereof has been found to completely deteriorate over a period of time. Still further, a wedge formation of earth and sand has been formed within the area designated P, and consequently, such earth and sand, under pressure, has tended to enter the space or gap defined between the seal and the end surface of the bushing, the result being the deleterious loss of the effective sealing properties.